They are more likely to appear only during certain months of the year. I forget which one but it should be mentioned in your Clan Primer under the Pesky Reds section.

Also, if you have high levels/abilites try to get a fight with a Red Chocobo at level 99 as beating him (even capturing him with a Choco Knight) nets you a special accessories that allows you to summon one of the Espers when your smash gauge is full.